Illuminators project an output pattern from a light source onto an illumination area. The key to making an effective illuminator is to direct as much of the light from the light source to the illumination area as possible while minimizing the amount of light directed or scattered elsewhere. There are many ways of directing light including reflectors, spherical lenses, aspheric lenses, Fresnel lenses, diffractive optics and lens arrays.
A microlens array is an array of small spherical or aspheric lenslets. Each lenslet in a microlens array produces its own output pattern according to its aperture dimensions, surface curvature, and the divergence of the incoming light from the source. If the output patterns of all the lenslets are summed, the total output pattern of the illuminator is obtained. If, for example, every lenslet in a microlens array has the same output pattern, the total output pattern has an intensity profile similar to that of the individual lenslet. Although this type of microlens array is excellent for disposing of most structure inherent in the light source, it is difficult or impossible to tailor the shapes of the output patterns.
Prior art microlens arrays have only two types of space-filling regular symmetries: four-fold and six-fold. At all but the smallest of aperture sizes compared to the focal lengths of the lenslets, four-fold or rectangularly symmetric, spherical microlens arrays, have an undesirable "dogbone-shaped" output pattern. Six-fold or hexagonally symmetric microlens arrays are usually limited to hexagonal or circularly-shaped output patterns. A more flexible means of tailoring the output pattern of an illuminator to fit the intended use is needed. Microlens arrays which produce even illumination with asymmetric or irregularly-shaped output patterns would be particularly useful.